The present invention relates generally to a portable ultrasonic Doppler system for sensing movement, and more specifically to such apparatus adapted for monitoring fetal heart rate.
The Doppler effect was first described in the 19th century by Austrian physicist Christian Doppler. In exlaining the Doppler effect, reference is often made to the pitch of the whistle of a moving train. When a train with its whistle blowing moves toward a stationary listener, the pitch of the whistle is higher than if the train were motionless. When the train moves away from the listener, the pitch of the whistle becomes lower. Ultrasonic Doppler probes used in fetal mointoring operate by the same principal. Such a probe includes a transmitter crystal which emits an ultrasonic signal. The term "ultrasonic" means that the signal is higher in frequency than the highest sound that can be heard by the human ear, in other words, above 20,000 cycles per second. The Doppler probe is held against the mother's skin over the position of the fetal heart. The transmitter crystal sends its ultrasonic signal into the mother's body, and the signal is reflected back from the moving fetal heart to a receiving crystal in the Doppler probe. The movement of the fetal heart modifies the reflected frequency according to the heart velocity. This frequency shift is converted to an audible signal which is amplified so that it can be heard by a doctor. The ultrasonic Dopper technique is not limited to monitoring fetal heart rate. It is also useful, for example, in listening to the flow of blood through the arteries, as well as other movements within a living body. Such techniques can also be used to listen to other moving parts, e.g., in machines.
Electronic fetal monitoring is a routinely applied technique in the care of patients both prior to and during labor and delivery. Fetal heartbeats can be detected from the interior abdominal wall indirectly by means of a set of electrodes which pick up the weak fetal electrocardiogram on the maternal abdomen, a sensitive microphone which picks up fetal heart sounds, or an ultrasonic Doppler transducer which detects Doppler frequency shifts in ultrasonic energy reflected from moving components of the fetal cardiovascular system. Stethoscopes have also been used to listen to the fetal heartbeat.
The use of stethoscopes for listening to the fetal heartbeat has been unsatisfactory due to the high degree of extraneous or artifact noise which occurs during periods of labor contractions. Even prior to the commencement of labor, ordinary stethoscopes have been unsatisfactory because the sound of the fetal heart can be masked by the sound of the mother's heartbeat.
Ultrasonic Doppler systems for monitoring fetal heart rate are well known; however, those systems presently available are inconvenient to use. Most of the ultrasonic Doppler systems available to date include an ultrasound probe together with processing circuitry which is attached by wires to an earphone used by the physician. Other known systems utilize Doppler probes which are hard-wired to speakers which, for example, can be clipped to the physician's shirt pocket. An example of such a system is the model D100 Pocket Fetal Heart Detector sold by Sonicaid, Inc. of Fredericksburg, Va. The disadvantage to such systems is that the wires connecting the Doppler probe to the speaker or earphone can become tangled and get in the way during the physician's examination of the patient.
In order to overcome the inconvenience associated with hard-wired units, radiotelemetry systems have been proposed for clinical fetal monitoring. One such system is discussed in an article entitled "A Two-Channel Radiotelemetry System for Clinical Fetal Monitoring," by Michael R. Neuman and Edward O'Connor, BIOTELEMENTRY PATIENT MONITORING 7:104-121 (1980). In the system disclosed in this article, the fetal electrocardiogram is picked up by a scalp electrode and transmitted over a two-channel radio system to a separate receiver. The transmitter is packaged in a case and strapped to the patient's thigh. The system disclosed does not utilize an ultrasonic Doppler probe and, because its size requires it to be strapped to the patient, it is somewhat clumsy. Other known radiotelemetry systems for fetal monitoring are also bulky and therefore are inconvenient to use.
It would be advantageous to provide an ultrasonic Doppler system for monitoring movement, such as fetal heart rate, which is both portable and convenient to use. The separate components of such a system should not be interconnected by wires which can get in the way and become tangled. The Doppler probe should be easy to hold and adaptable to a variety of ultrasonic transducer configurations. It would be further advantageous for such a system to provide for both ultrasonic Doppler monitoring and conventional stethoscope-type direct sound monitoring. It would also be desirable to provide a means for recording the information sensed by such a system, and even to record the comments of a physician who is using the system.
The present invention relates to such a system.